The present invention relates to a method of passifying the surface of a reactive metal sponge regulus.
Reactive metals of Group IVB, including zirconium, hafnium and titanium, are industrially produced from suitable ores by carbochlorination of the ores at high temperatures to produce a tetrachloride powder. The tetrachloride powder is then reduced with magnesium, calcium, sodium or other like metal to form a metal sponge regulus. The sponge regulus is then vacuum distilled at high temperatures to remove the contaminants and subsequently crushed to small particles suitable for further processing.
Reactive metals are highly pyrophoric as are some of the contaminants in the sponge regulus. Thus, a high surface area sponge regulus is subject to fires upon exposure of the distilled sponge regulus to the atmosphere or during the crushing step after the vacuum distillation step. In addition, chemistry specifications for commercial products severely limit the maximum permitted contamination of oxygen and nitrogen, which are present in the air and readily react with these metals. If the metal contains excessive amounts of oxygen or nitrogen, the metal must be recycled. See, in this regard, U.S. Pat. Nos. 5,062,887; 5,078,789; 5,080,858 and 5,100,465 which disclose processes and equipment for vacuum distilling and subsequently handling zirconium sponge.